This application relates to and incorporates by reference Japanese Patent application No. 2002-3550, filed on Jan. 10, 2002 and Japanese application No. 2001-105159, filed on Apr. 3, 2001.
This invention relates to a vapor compression type refrigeration apparatus that has means for estimating the amount of refrigerant remaining in the cycle. This invention is effective for use in vehicle air-conditioning systems.
In a typical refrigeration apparatus used in a vehicle air-conditioning system, lubricating oil is mixed in the refrigerant, and the lubricating oil is circulated together with the refrigerant for lubrication of the movable and sliding members in the compressor.
However, if refrigerant leaks from a rubber hose, pipe joint or other location, and the amount of refrigerant remaining in the circuit decreases, the amount of refrigerant drawn into the compressor also decreases. Since the amount of lubricating oil supplied to the compressor decreases, serious damage such as seizure may occur in the compressor.
Conventionally, the pressure in the refrigeration circuit is detected. If the detected pressure is lower than a predetermined value (for example, 0.3 MPa), the amount of refrigerant remaining in the cycle is regarded as having decreased below the predetermined level, and the operation of the compressor is suspended.
Even when there is a refrigerant leak, the pressure inside the refrigeration system does not fall as long as the liquid refrigerant exists in the system because the refrigeration cycle occurs in a closed system. That is, the liquid refrigerant evaporates in the gas-liquid separator to maintain the saturation pressure.
The pressure on the lower pressure side of the refrigeration system does not start decreasing unless the refrigerant leak continues even after all the liquid refrigerant in the refrigeration system has evaporated. Thus, when the pressure on the lower pressure side becomes lower than a predetermined value, the amount (weight) of refrigerant remaining in the system has already become significantly lower than normal.
As a result, according to the conventional method of monitoring pressure in the refrigeration system, damage to the compressor may occur because a refrigerant leak, if one occurs, cannot be detected until the amount of refrigerant remaining in the system has significantly decreased from the normal level.
Particularly, when the refrigerant leaks little by little (a so-called slow leak), there is a fear that the compressor will be seriously damaged if the amount of remaining refrigerant becomes approximately 50% or less than the normal level. Thus the leak must be detected before the amount of remaining refrigerant has become 50% or less than the normal level. However, according to the conventional method of monitoring the pressure in the refrigeration circuit, it is very difficult to detect a refrigerant leak before the amount of remaining refrigerant has become about 10% or less than the normal level.
This invention has been made to solve these problems, and its object is to detect refrigerant leaks at an early stage.
Basically, according to a first aspect, the invention is a vapor compression type refrigeration apparatus that includes a compressor (21), a condenser (22), a decompressor (24) and an evaporator (25). The apparatus, cools a high-temperature, high-pressure refrigerant compressed with the compressor (21) with the condenser (22) and evaporates low-temperature, low-pressure refrigerant decompressed with the decompressor (24). An amount of refrigerant remaining in the refrigeration circuit is determined by comparing an actual parameter (xcex94T) related to actual heat dissipation (Q) in the condenser (22) and a theoretical parameter (ixcex94T) related to heat dissipation (iQ) in the condenser (22).
Since the difference between the theoretical heat dissipation (iQ) in the condenser (22) and the actual heat dissipation (Q) in the condenser (22) becomes large as explained later, a decrease in refrigerant can be precisely detected, even when the amount of refrigerant has only slightly decreased from the normal level in the refrigeration circuit. Refrigerant leakage can thus be detected relatively early.
If refrigerant leakage is detected based on the heat dissipation on the condenser (22) side, it is not necessary to consider the generation of condensed water, or latent heat, as explained later. Thus, the parameters related to the heat dissipation on the condenser (22) side can be calculated with accuracy.
A vapor compression type refrigeration apparatus according to a second aspect of the present invention includes a compressor (21), a condenser (22), a decompressor (24) and an evaporator (25). The apparatus, cools a high-temperature, high-pressure refrigerant compressed with the compressor (21) with the condenser (22) and evaporates low-temperature, low-pressure refrigerant decompressed with the decompressor (24). The apparatus further includes actual heat dissipation parameter calculation means (18c, 18d) for calculating a parameter (xcex94T) related to actual heat dissipation (Q), theoretical heat dissipation parameter calculation means (S150) for calculating a theoretical parameter (ixcex94T) related to heat dissipation (iQ) in the condenser (22) based on data provided when a normal level of refrigerant exists in the refrigeration circuit, and remaining refrigerant amount determination means (S160) for determining an amount of refrigerant remaining in the refrigeration circuit by comparing the parameter (xcex94T) calculated by the actual heat dissipation parameter calculation means (18c, 18d) and the parameter (ixcex94T) calculated by the theoretical heat dissipation parameter calculation means (S150).
Since the difference between the theoretical heat dissipation (iQ) in the condenser (22) and the actual heat dissipation (Q) in the condenser (22) becomes large as explained later, a decrease in refrigerant can be precisely detected, even when the amount of refrigerant has only slightly decreased from the normal level in the refrigeration circuit. Refrigerant leakage can thus be detected early.
If refrigerant leakage is detected based on the heat dissipation on the condenser (22) side, there is no need to consider the generation of condensed water, or latent heat, as explained later. Thus the parameters related to the heat dissipation on the condenser (22) side can be calculated accurately.
A vapor compression type refrigeration apparatus according to a third aspect of the present invention includes a compressor (21), a condenser (22), a decompressor (24) and an evaporator (25). The apparatus, cools a high-temperature, high-pressure refrigerant compressed with the compressor (21) with the condenser (22) and evaporates low-temperature, low-pressure refrigerant decompressed with the decompressor (24). The apparatus further includes actual heat dissipation parameter calculation means (18c, 18d) for calculating a parameter (xcex94T) related to actual heat dissipation (Q), theoretical heat dissipation parameter calculation means (S150) for calculating a theoretical parameter (ixcex94T) related to heat dissipation in the condenser (22) based on a physical quantity (Te), which is related to an evaporation temperature of refrigerant in the evaporator (25) when a normal level of refrigerant exists in the refrigeration circuit, and remaining refrigerant amount determination means (S160) for determining an amount of refrigerant remaining in the refrigeration circuit by comparing the parameter (xcex94T) calculated by the actual heat dissipation parameter calculation means (18c, 18d) and the parameter (ixcex94T) calculated by the theoretical heat dissipation parameter calculation means (S150).
In this way, since the difference between the theoretical heat dissipation (iQ) in the condenser (22) and the actual heat dissipation (Q) in the condenser (22) becomes large as explained below, a decrease in refrigerant can be precisely detected, even when the amount of refrigerant has only slightly decreased from the normal level. Refrigerant leakage is thus detected early.
If refrigerant leakage is detected based on the heat dissipation on the condenser (22) side, there is no need to consider the generation of condensed water, or latent heat, as explained later. Thus the parameters related to the heat dissipation on the condenser (22) side can be calculated accurately.
It is preferred to use the difference between a temperature related to the refrigerant temperature inside the condenser (22) and the temperature of cooling air sent to the condenser (22) for the actual parameter (xcex94T) and theoretical parameter (ixcex94T).
The temperature difference of cooling air across the condenser (22) may be used as the actual parameter (xcex94T) and theoretical parameter (ixcex94T).
As described later, if there is an insufficient amount of refrigerant, the suction pressure of the compressor (21) changes significantly. Thus, refrigerant leakage can be more precisely detected by taking the suction pressure of the compressor (21) into account in the calculation of the theoretical parameter (ixcex94T).
Also as described later, if there is an insufficient amount of refrigerant, a specific enthalpy change (ixcex94H) of refrigerant in the condenser (22) changes significantly. Thus, refrigerant leakage can be more precisely detected by taking the specific enthalpy change (ixcex94H) of refrigerant in the condenser (22) into account in the calculation of the theoretical parameter (ixcex94T).
Furthermore, the theoretical parameter (ixcex94T) may be calculated based on the suction pressure of the compressor (21) and also may be based on a specific enthalpy change (ixcex94H) of refrigerant in the condenser (22). Refrigerant leakage can thus be detected more precisely.
A vapor compression type refrigeration apparatus according to a fourth aspect of the present invention includes a compressor (21), a condenser (22), a decompressor (24) and an evaporator (25). The apparatus, cools a high-temperature, high-pressure refrigerant compressed with the compressor (21) with the condenser (22) and evaporates low-temperature, low-pressure refrigerant decompressed with the decompressor (24). An amount of refrigerant remaining in the refrigeration circuit is determined by comparing an actual parameter related to actual heat absorption in the evaporator (25) and a theoretical parameter related to heat absorption in the evaporator (25).
Since the difference between the theoretical heat absorption and the actual heat absorption becomes large, a decrease in refrigerant can be precisely detected, even when the amount of refrigerant has only slightly decreased from the normal level in the refrigeration circuit. Refrigerant leakage can thus be detected at an early stage.
The compressor (21) may be a variable-capacity type compressor that controls the displacement such that the discharging rate becomes equal to a predetermined value, or a variable-capacity type compressor that varies the displacement based on the pressure difference across a throttle in the refrigerant circuit.
If a variable displacement compressor is used, it is preferred to calculate the theoretical parameter (ixcex94T) based on the smaller of a refrigerant flow rate calculated based on 100% compressor capacity and a maximum flow rate determined at least based on the discharge pressure of the compressor (21).
The reference numbers above are exemplary and correspond to the specific parts described in the illustrated embodiments described below.